This invention relates to liquid crystal display devices viewed in reflection, and, more particularly to a liquid crystal reflection display device in which direct current can be utilized with extended electro-optical lifetime for the liquid crystalline material.
Generally speaking, electro-optical systems employing liquid crystalline materials in contact with an electrode or a photoconductive layer enjoy a wide range of applications but have heretofore been limited in duration of operation and the electrode or photoconductive layer. This duration of lifetime has been particularly limited in cells having a photoconductive layer in contact with the liquid crystalline layer. Prior attempts to prevent or retard degradation of such devices have included the use of a barrier layer such as the cellulose nitrate barrier layer disclosed in U.S. Pat. No. 3,722,998; the polymer barrier layers disclosed in U.S. Pat. No. 3,795,516 and U.S. Pat. No. 3,795,517; the tributyltin oxide barrier layers disclosed in U.S. Pat. No. 3,894,794 and U.S. Pat. No. 3,894,793; and by silicon dioxide disclosed in U.S. Pat. No. 3,869,195, U.S. Pat. No. 3,674,342 and U.S. Pat. No. 3,647,280.
A layer of titanium dioxide is utilized in U.S. Pat. No. 3,748,018 to allow selective operation of a liquid crystal display in either the transmission or reflectance mode. Although a portion of the layer of titanium dioxide is in contact with the layer of liquid crystalline material at the terminal ends of the liquid crystal display, the titanium dioxide layer does not appear to be part of a dielectric mirror located between the electrode and the liquid crystal layer.
U.S. Pat. No. 3,853,386 discloses a low-loss highly reflective multi-layer system comprising alternate layers of high refraction and low refraction oxide layers wherein the at least last three high refraction layers comprise zirconium oxide. Otherwise, titanium dioxide and silicon dioxide are included in the alternate layer structure in addition to the zirconium oxide layers; however, the titanium dioxide layer is the first layer on the substrate in the alternate layer structure so that without the zirconium oxide layer as the terminal layer, the silicon dioxide layer would be in contact with any imaging layer were the dielectric mirror thus modified inserted into a display device.
Jacobson et al in an article entitled "A Real-Time Optical Data Processing Device", beginning at page 17 of the September, 1975 issue of Information Display, disclose an alternating current photoactivated liquid crystal light valve incorporating a dielectric mirror consisting of alternate quarter wavelength films is insulating, direct current can not occur. Furthermore, sputter-deposited films of silicon dioxide overcoat the dielectric mirror to provide an alignment function and a buffer to prevent electro-optical degradation.
In new and growing areas of technology such as liquid crystal imaging, new methods, apparatus, compositions, and articles of manufacture are often discovered for the application of the new technology in a new mode. The present invention relates to a novel liquid crystal display device for extending the electro-optical lifetime of liquid crystal layers utilized therein.